Rotation screen printing machine and squeegee device

ABSTRACT

A rotary screen printing machine of the type including at least one cylindrical stencil, each with a squeegee blade for forcing a printing fluid such as paint or paste through apertures in the stencil onto a textile web or sheet of paper. The squeegee of the present invention is formed as a thin flexible metal strip having a thickness less than 1% of the width of the portion of such strip protruding from its holder. The squeegee blade is suspended at two locations mounted in a holder, at least one location having transverse slot permitting lateral expansion and contraction to compensate for vertical deflection of the blade or of the holder.

RELATED APPLICATION

This application is a continuation-in-part of the copending applicationSer. No. 811,787 filed on Apr. 1, 1969, now abandoned by the same-namedapplicant.

The invention relates to a rotary screen printing machine provided withsupporting members for the ends of one or more cylindrical stencils andwith suspension members for a squeegee device disposed within thestencil and consisting of a squeegee holder with a fitting for aflexible squeegee blade, and with means for guiding the material to beprinted. Different embodiments of such a machine are known in which itis always desired to construct the machine as wide as possible in orderto permit the printing of a broad web or loose sheets.

However, there have been limits to the broader construction of themachine because to the deflection of the squeegee. This deflectioncauses a difference in the squeegee pressure of the central portion withrespect to the outer portions of each cylindrical stencil. A seconddifficulty was experienced in that owing to the great length of thesqueegee, its weight increased in such a way that trouble wasencountered on pulling the squeegee device from and sliding it againinto the cylindrical stencil, which is occasionally required.

It is an object of the invention to provide a machine provided with alight-weight squeegee device so that a very wide machine can beassembled therewith. This object is attached according to the inventionin that the squeegee blade consists of a very thin steel strip thethickness of which is less than 1% of the width of the portion of thestrip which freely protrudes from the fitting and greater than 0.1% ofthis width.

It has appeared by experiment that this squeegee blade can easily curveor deform in the direction of rotation of the stencil, whereby a lowfrictional resistance with the inner side of the stencil is produced.This deformation of the squeegee is already possible at a minorpressure, so that consequently the deflection of the squeegee holderunder this pressing force is limited to a minimum.

It has further appeared that the new squeegee blade allows for an idealdeformation so that an angle of pressure ranging from 90° to 3° can beadjusted, which range is beyond the limits usually obtainable with theconventional squeegees. The squeegees blade is no longer liable tochemical corrosion due to solvents in the printing mass. The steelsqueegee blade is naturally stiffer in its own plane than the previouslyused rubber squeegee blade, so that also in this respect a lighterconstruction can be applied, but, nevertheless, a sufficient bendingstrength (rigidity) in a vertical plane is obtained.

The invention relates especially to a machine in which each squeegeeholder cooperates with suspension members situated outside both ends ofthe stencil. A machine constructed in this way is distinguished in thatthe squeegee blade with its fitting is supported by the squeegee holderat two locations. By a correct selection of the suspension points, thedeflection of the squeegee holder in a vertical plane will be minimalwhen the squeegee is downwardly loaded. The mass inertia moment of thesqueegee holder may now be taken considerably smaller than that of theconventional squeegee holder. Since the load owing to the squeegeepressure is smaller with the invention than in the conventionalconstruction, the total load is considerably smaller than previously sothat for that reason a lighter construction is possible and therefore agreater breadth of the machine can be achieved while maintaining auniform pressure of the squeegee along the entire length of thecylindrical stencil which is generally about 1.5 meters and preferably2.0 or even 2.4 meters.

It is a further object of the invention to provide means to position thepressure area of the squeegee blade permanently in essentially a fixeddesired zone of the stencil nothwithstanding adjustments in the pressureangle of the blade. This zone may lie either exactly above the zone ofcontact between the stencil and the web or at a short distance before orbehind that zone.

The aforementioned and further objects of the invention will hereinafterbe described with reference to the accompanying drawings which areexemplary, showing a few embodiments of the squeegee device according tothe invention, wherein:

FIG. 1 shows a cross-section of a stencil provided with this squeegeedevice according to a first embodiment;

FIG. 2 shows to a considerably smaller scale a side elevation of acomplete squeegee device;

FIG. 3 is another embodiment of the squeegee device in a sectioncorresponding to FIG. 1;

FIG. 4 shows a detail of the squeegee device according to a thirdembodiment;

FIGS. 5 and 6 show a front view of the two suspension points of thesqueegee with its fitting to the holder in the embodiment according toFIG. 4;

FIGS. 7-9 show the influence of the location of the pressure area of thesqueegee.[.; and.]..Iadd...Iaddend.

.[.FIG. 10 are diagrams showing the deflection of the blade in the priorart (a) and according to the present invention (b)..].

The rotary screen printing machine to which this invention relates is ofthe type as described, e.g. in the U.S. Nos. 3,291,044, 3,304,860,3,313,232 and 3,420,167. In such a machine e.g. twelve or sixteenjuxtaposed supporting members are provided for the ends of as manycylindrical stencils. For the sake of simplicity all this is notrepresented in the drawings.

The machine is likewise provided with suspension members 1 for thesqueegee device 2 within each stencil. The latter device consists of asqueegee holder 3 provided with a fitting 4 for a flexible squeegeeblade 5. The machine is further provided with means such a roller 6 forguiding the material to be printed. When this material is sufficientlyrigid in itself, it may directly bear on the means 6 embodied assupporting rollers, but in the case of weak material, like e.g. textile,a supporting belt 7 can be applied in the usual way.

In the previously known machines the squeegee blade mostly consists ofrubber or other such flexible material. According to the presentinvention the squeegee blade 5 consists of a thin metal strip ofstainless steel or spring steel the thickness of which is less than 1%of the generally vertical width of the portion of the strip which freelyprotrudes from the fitting 4, and greater than 0.1% of this width. Ifdesired, it is also possible to apply a strip of synthetic material,provided this material has an elastic flexibility analogous to that ofmetal. Such a material may be Vulkolan or Teflon, depending on the typeof paste or paint used.

The suspension members 1 each consist of a pneumatic cylinder (see FIG.2) the piston of which is pivotally secured to the squeegee device bysuitable bearing means, by which means the squeegee device 2 can belifted and lowered in order to release the squeegee blade 5 from thecylindrical stencil 8 or bring it again into contact therewith. Thelower position of the squeegee device 2 and as a consequence the angleat which the blade 5 exerts its printing function is adjusted by the aidof the adjusting nut 9.

As is visible in FIG. 2, each squeegee blade 5 is via its fitting 4supported at two locations 10 and 11 by the squeegee holder 3. Thisholder is constructed as a tube serving as a printing paste or paintfeeding conduit.

The locations 10 and 11 are so selected with respect to the ends of theholder 3 that the deflections .[.(d₂).]. at the ends of the blade 5 arealmost equal to the deflection .[.(d₃).]. of the blade at its center.Both of these values of deflection are considerably less than themaximum deflection .[.(d₁).]. resulting when the blade 5 is securedalong its entire length to the holder 3. .[.These deflectionrelationships can be best seen in FIG. 10..].

Means 12 are provided in each squeegee device 2 cooperating with thesqueegee-holder 3 in order to displace the latter in a generallyhorizontal direction during its height adjustment in such a manner, thatthe pressure area 13 of the squeegee blade 5 is always situated in asubstantially fixed zone of the stencil that is to say the zone which isin touch with the material to be printed, or a region at a shortdistance before or after that zone. These means 12 consist of an arm 14outside at least one end of the stencil 8.

This arm 14 is connected at its one end 15 with the squeegee holder 3,and is pivotally supported at its other free end 16. Since in thisembodiment the suspension members 1 exclusively allow a verticaldisplacement of the squeegee holder 3, the end 16 of the arm 14 canundergo, via the bracket 17, a limited shifting in a direction parallelto the travel of the material to be printed, that is to say, of the belt7. This construction causes a turning of the squeegee holder 3 onlowering the squeegee device 2 and a tilting of the supporting locations10 and 11 and consequently of the fitting 4 in such a manner that thepressure area 13 of the squeegee blade 5 remains within the correctregion.

In the embodiment according to FIG. 3 the suspension members 1 arepivoted at 18 to the frame of the machine. Each suspension member 1 issecured to the squeegee holder 3 by means of a clip 19 which looselysurrounds the holder 3 and permits striding rotational movement thereofrelative to the dip 19. These clips are situated outside the ends ofeach stencil 8 and are each pivotally connected with one end of an arm21 through a tenon 20. Each arm 21 has at its free end 22 a point ofsupport 24 pivotable about a fixed axis which however is adjustable bymeans of a nut 23. These elements 19-24 constitute an equivalent of themeans 12, as described with reference to FIG. 1.

FIG. 4 shows an embodiment of one of the supporting locations 10 or 11at which the fitting 4 of the squeegee blade 5 is supported by thesqueegee holder 3. FIG. 5 shows a view of the supporting location 10 atwhich the fitting is fixed to the holder 3 for rotation therewith. Thesupporting location 11 depicted in FIG. 6 is provided with an elongatedhole 25 in the connecting strips 26, so that there is a limitedpossibility of longitudinal movement between the fitting 4 and theholder 3 to allow for differences in the bowed lengths of these undervertical pressure.

This limited possibility of relative displacement is of importancebecause the vertical deflection of the squeegee holder or paint feedingconduit 3 is generally different from the corresponding verticaldeformation of the combination fitting 4 with squeegee blade 5 resultingin different lengths of these when bowed by application of verticalpressure against the stencil 8.

FIG. 7 shows the situation in conformity with the FIGS. 1 and 3, a paintimprint 28 being formed on the web 27 to be printed, the imprint beingpartially on and in the web (see FIG. 7A). When the layer of paintshould be entirely on the web and the penetration of the paint into theweb should be reduced to a minimum, the pressure area of the squeegee 5should be slightly shifted to behind or beyond the point according toFIG. 7. This situation is attained by unscrewing slightly the nut 23from the construction according to FIG. 3. Should it be desired for thepaint to be entirely pressed into the web, then the arm 21 of FIG. 3 isslightly shortened so that the conditions according to FIG. 9 occur.

The advantages of the machine according to the invention can besummarized as follows:

the occurring forces and the weight of the squeegee device can bereduced in such a considerable manner, that the width of the machine canbe increased without the risk of a harmful vertical deflection of thesqueegee that is to say without light and dark coloured zones beingproduced on printing,

the friction between the steel squeegee and the nickel stencil is lessthan with a rubber squeegee, which is favorable from the viewpoint ofwear and tear and consequently for the life of the squeegee device andthe stencil,

the metal squeegee allows a particularly great variation in pressureangle ranging between 90° and about 3°,

using a metal squeegee requires a much smaller force for applying thesame amount of paint than in case of a conventional squeegee, whichcontributes to obtaining a light weight construction,

the two-point suspension of the squeegee results in smaller maxima ofthe deflection of the squeegee than with the conventional securing ofthe squeegee along its entire length,

no chemical corrosion is produced in the case of a metal squeegeebecause stainless steel can be utilized, but also spring steel which hasbeen subjected to a special surface treatment, such as a surface coatingto reduce chemical corrosion.

It will be understood that this invention is susceptible to modificationin order to adapt it to different usages and conditions, andaccordingly, it is desired to comprehend such modifications within thisinvention as may fall within the scope of the appended claims.

What is claimed is:
 1. A rotary screen printing machine having a frame,supporting members for the ends of one or more cylindrical stencils andwith suspension members mounted on the frame for a squeegee devicedisposed within the stencil and consisting of a squeegee holder with afitting for a flexible squeegee blade, and with means for guiding thematerial to be printed; the improvement consisting in that the squeegeeblade consists of a thin flexible metal strip, the thickness of which isless than 1% of the width of the portion of the strip which freelyprotrudes from the fitting, said squeegee holder being supported atleast on one end by suspension members and the squeegee blade with itsfitting being supported by the squeegee holder .[.at two spacedlocations.]., the suspension members of each squeegee holder comprisingmeans for adjusting the height of the squeegee blade within the stencil,and further comprising means connecting the squeegee holder with theframe and permitting displacement of the holder in a generallyhorizontal direction, parallel to the guiding direction of the materialto be printed during the adjustment for height, in such manner that thepressure area of the squeegee blade is situated permanently in asubstantially fixed desired zone of the stencil.
 2. A machine accordingto claim 1 whereby said .[.lastnamed.]. .Iadd.last-named .Iaddend.meanscomprises an arm outside at least one end of the stencil, said arm beingconnected at one end thereof, to said squeegee holder and being pivotedat the other end thereof to the frame.
 3. A machine according to claim2, wherein the suspension members exclusively permit a verticaldisplacement of the squeegee holder, said one end of said arm beingrigidly secured to said squeegee holder, said other end of said armbeing slidingly mounted in said frame for limited sliding movement in agenerally horizontal direction as well as pivoting movement.
 4. Amachine according to claim 2, wherein said one end of said arm ispivotally secured to said squeegee holder, said other end of said armbeing pivotally connected to the frame by a fixed pivot.
 5. A machineaccording to claim 4, further comprising means for shifting the positionof said pivot. .Iadd.
 6. A machine according to claim 1 wherein saidsqueegee blade with its fitting is supported by the squeegee holder attwo spaced locations. .Iaddend.